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Calgary’s urban canopy weathers drought, smoke in steamy Alberta summer

Despite the record-breaking heat in Calgary this summer, the city’s tree canopy is in healthy condition, said the city’s urban forestry lead.

In Wednesday’s transportation and transit meeting, Coun. Druh Farrell brought up trees and how they impact how we travel without cars (walking, cycling). We need to pay particular attention to the impact a changing climate may have on them, Farrell said.

Farrell mentioned that this year’s heat and drought caused the loss of tree canopy in Calgary.

Julie Guimond, urban forestry lead for the City of Calgary said that no trees have died as a result of this year’s heat.  Though, there have been individual cases of trees struggling with the conditions.

“No, we haven’t seen the impact at the canopy and the forest level – so, the totality of all of the trees,” Guimond said. There are more than 500,000 trees in the city’s inventory, all tagged with a GIS marker.

Guimond said trees are very hardy perennials. Protected by wood and bark, the trees hold in them a reserve that protects against years like this past one.

Calgary has had nearly 20 days of 30 C or higher temperatures this summer. Typically, we get five days with that heat.  

When trees are pressed for water and nutrients in a given year, they draw on the built-up reserves in their system.

“It’s just like as if we have one really late night or really early morning – we’re tired that day,” said Guimond.

“But we can sort of get back on to a better schedule and rebuild our own personal reserves, and a tree is going to respond the same way.”

Fall is a critical time

Guimond said the city waters trees for the first five years through establishment. Even with recent wetter, cooler weather, they’ll continue to water those city trees this fall.

“This is the time which trees are growing the root system. They’ve already put their leaves on for next year, the buds are already in place,” she said.

The water is able to build up around the roots in fall, Guimond said, which helps stimulate that reserve production for future stressful years.

Right now, you can water trees slowly, once a week for maximum benefit for next year, Guimond said.

For more Tree Care info, Visit calgary.ca/trees

They’re keeping irrigation on in parks to help preserve trees. They also look at some of the significant trees in the city or ones in stressful areas, like along boulevards or centre medians for extra attention.  

Guimond also said the type of trees predominant in Calgary help, too.

“The great thing about poplars is they’re native, they’re adapted to this environment, so they’re used to the oddities that are Calgary’s weather,” she said.

Plus, in the larger banks of trees in Calgary, there are microclimates. That might impact trees in different ways.

The city monitors many of these factors to ensure the ongoing health of the urban canopy.

Rubber sidewalks

One of the ways they’re helping protect tree roots in Calgary is through a pilot project involving rubber sidewalks.

Yes, rubber.

City of Calgary roads director Troy McLeod brought up the recycled rubber sidewalk pilot that’s ongoing in the city during that same transportation meeting.

Several locations in Calgary now have poured rubber sidewalks. Similar looks to concrete, but not the same. CITY OF CALGARY

Later, McLeod expanded upon how that program works.

He said in situations where tree roots were pushing up sidewalks, it was creating a tripping hazard and the city would try to fix these areas. When they had to fix them, it risked damaging the tree root and could kill the tree.

“This application works really well because we can use a flexible material, it’s obviously got an ability for moisture to get through, and so it’s a really good alternate application for this situation,” he told LiveWire Calgary.

When thinking about that tree’s reserves, Guimond said this new system protects that. But, if a tree is damaged or dying, they just replace it along with a concrete sidewalk.

“If we think that that tree has a long lifespan left, then that’s a great opportunity for us to put that flexible sidewalk over top with the roads teams so that we can protect those roots. Root protection is one of the biggest pieces for us when it comes to protecting trees,” she said.

The rubber sidewalks pilot could expand beyond the current 15 sidewalks they have. While it protects the tree roots, it’s also cheaper than concrete and provides environmental benefits.

McLeod said while the current sidewalks have already wintered once, they’re collecting more data to see how they stand up to multiple bitter winters before pushing ahead. After they assess costs (including maintenance) this environmental solution may become more common.

Locations of rubber sidewalks:

  • Temple Drive between 56 and 61 Street NE
  • Rundle Drive
  • Cabot Street SW (13 Avenue)
  • 31 Avenue and 60 Street NE
  • 21 Avenue – 20 Street NW
  • 24 Avenue – 20 Street NW
  • RiverValley Drive SE
  • 19 Street and 69 Avenue SE

There are roughly 110 lineal metres in total, McLeod said.

Smoky threat?

With the blistering heat often comes tinder dry conditions and the threat of forest fires. This summer, that left Calgary with several days of apocalypse-like skies that choked out the sunlight.

Guimond said while they haven’t dug into whether there’s a change in chemistry in trees with heavy amounts of smoke in the air, there was a silver lining to the haze.

“We haven’t seen an impact from the smoke specifically, but what we have seen is a reduction in some ground temperatures because the sun isn’t as strong on the ground,” she said.

“That helps in retaining some of the moisture around those trees so from a watering-of-the-tree standpoint, it probably has helped.”

Guimond said she expects more research work to come out on the impact of the smoke on trees. Given the prevalence of it, it’s something they’re keeping their eye on.

Sustained drought the likely catalyst for canopy decline

This was a summer of intense heat and drought. While there’s certainly climate change as a backdrop, for now, it’s just this year, Guimond said.

“At this point, there’s not enough time, enough years in a row for this to become the updated climate,” she said.

In the meantime, Guimond said they’re experimenting with an injection watering method to reduce potential surface evaporation should temps continue their climb.

There’s evidence of the impact of prolonged drought on some city spruce trees. Guimond said about four years ago there had been a string of two or three years with drought-like conditions.  They were showing signs of deteriorating health.

They’ve since been monitoring and testing the trees with results coming back negative.

“It really just comes down to that long-term impact of those multiple years of drought that hit that specific species. Those are the pieces we’re going to continue to monitor.”